1. Technical Field
The present technology relates to a pneumatic tire in which a plurality of loop-shaped narrow grooves are concentrically disposed in a tread portion, and particularly relates to a pneumatic tire by which braking performance and turning performance on ice can be enhanced.
2. Related Art
Conventionally, many drainage grooves and/or sipes are provided in the tread portion of pneumatic tires that are expected to run on ice in order to increase performance on ice based on the edge effects of these drainage grooves and/or sipes. Specifically, the edge components in the tire width direction that resist slipping in the tire circumferential direction contribute to enhancing braking performance on ice, and the edge components in the tire circumferential direction that resist slipping in the tire width direction contribute to enhancing turning performance on ice.
In light of this understanding, providing loop-shaped sipes that (when viewed planarly) curve in circular, polygonal, or spiral-like manner in a tread portion has been proposed for the purpose of diversifying the extending direction of the edge components of the tread portion and enhancing braking performance and turning performance on ice (e.g. see Japanese Unexamined Patent Application Publication No. H05-178028A, Japanese Unexamined Patent Application Publication No. 2007-216816A, and Japanese Unexamined Patent Application Publication No. 2008-56206A).
However, with pneumatic tires provided with loop-shaped sipes in the tread portion, in cases when traveling on a road surface such as those where a water film is present on ice (when the air temperature is near 0° C.), water enters the sipes and, as a result, sufficient edge effects and water discharging effects of the sipes cannot be obtained. Particularly, sipes formed to have a loop-shape have few portions that are open to circumferential grooves and/or width direction grooves, and it is difficult to discharge water that was entered the sipes. Therefore, on roads such as those where a water film is present on ice, the expected functionality cannot be displayed. Thus, with the present technology, a definite enhancement of braking performance and turning performance on ice cannot be achieved.